Device for machining the surface of parts

ABSTRACT

Device for Processing the Surface of Objects The invention relates to a device ( 1 ) for processing the surface of objects ( 3 ) and comprises a predetermined number of processing stations (B 1 -B 8 ) performing processing processes and a conveying unit performing processing movements. The objects are transported into predetermined desired positions at the processing stations (B 1 -B 8 ) by means of the conveying unit. The device ( 1 ) further comprises a central controller ( 7 ), by means of which the processing movements of the conveying unit and the processing processes of the processing stations are synchronized by presetting a clock pulse being correlated with the processing movement of the object ( 3 ) to be processed and controlling the respective processing process via the central Is controller ( 7 ) for each processing station (B 1 -B 8 ).

The invention relates to a device according to the preamble of claim 1.

Such devices may generally serve for treating the surface of objects inthe form of varnishing processes, embossing processes, surface finishingprocesses, laser machining procedures and the like.

In particular, such devices may serve for printing objects. Theconveying unit may generally be configured such that it supplies theobjects to the individual processing stations by means of suitabletranslational and/or rotational movements.

When printing rotationally symmetrical objects, such as beverage cans,these are positioned on a rotary cycle apparatus and supplied to theindividual processing stations therewith. In order that the beveragecans thus transported to the processing stations may be placed in therespectively desired position with respect to the processing station,the beverage cans are disposed on rotatable supports. The supports arecoupled to a drive means, by means of which the beverage cans may berotated about their longitudinal axis.

For detection of the rotary positions of the beverage cans, incrementalencoders are disposed at the supports. The signals generated by theincremental encoders are transmitted to the processing stations so thatthe stations may be controlled in dependence upon the signals.

One disadvantage being that, on the one hand, the transmission of thesignals involves an undesirably great effort, since the signals of theincremental encoders must be transmitted from the supports rotating withthe rotary cycle apparatus to the respective stationary processingstations.

The further serious disadvantage arises that, due to the transmissionpaths, the signals of the incremental encoders are read into theprocessing stations with delay and are also subject to fluctuations.

Thus, undesired inaccuracies are caused when performing the processingprocesses in the individual processing stations. This in turn results ina non-satisfactory quality of the surface processing of the objects.

It is the object of the invention to provide a device of the kindmentioned at the beginning, by means of which a reproducible quality ofthe surface processing of the objects is obtained.

The features of claim 1 are provided in order to solve this object.Advantageous embodiments and expedient further developments of theinvention are described in the dependent claims.

The device for processing the surface of objects according to theinvention comprises a predetermined number of processing stationsperforming processing processes and a conveying unit performingprocessing movements, by means of which the objects are transported intopredetermined desired positions at the processing stations. In a centralcontroller, the processing movements of the conveying unit and theprocessing processes of the processing station are synchronized bypresetting a clock pulse being correlated with the processing movementof the object to be processed and controlling the respective processingprocess via the central controller for each processing station.

The basic idea of the invention thus consists in synchronizing theprocessing stations to the processing movements of the conveying unitvia the central controller. Thus, not only the effort of transmittinginformation between the processing stations and the conveying unit isreduced. Rather, by centrally presetting the clock pulse via the centralcontroller an exact activation of the processing stations is also madepossible. Inaccuracies owing to different transmission times of theposition values are largely eliminated. Furthermore, by generatingsuitable starting signals and predetermining the duration of thetransmission of the clock pulse to a processing station via the centralcontroller, the start and duration of the processing process performedin said processing station are accurately predetermined.

The device according to the invention may generally be used forperforming various surface treatments.

The device according to the invention is particularly advantageouslyemployed for printing rotationally symmetrical objects, which aresupplied to the processing stations on a rotary cycle apparatus andwhich are also rotatably journalled about their axes of symmetry.

In a particularly advantageous embodiment of the invention, a leadfrequency is generated as the clock pulse in the central controller, bymeans of which not only the processing stations but also the conveyingunit, in particular the drive means for effecting the rotation of theobjects on a rotary cycle apparatus, are activated. By this presettingof the lead frequency, a particularly simple and exact synchronizationof the processing stations and the elements of the conveying unit isachieved.

In a further advantageous embodiment of the invention, an individualclock pulse is generated for each processing station in the centralcontroller. This clock pulse is Is derived from the currently detectedposition values and detection times of the supply line of the respectiveobject to be processed.

In case of a conveying means configured as a rotary cycle apparatus, thecurrent rotary positions of the rotationally symmetrical objects, whichare rotatably journalled on the rotary cycle apparatus, are detected asposition values by means of incremental encoders. However, the signalsof the incremental encoders generated thereby are not transmitteddirectly to the processing stations for control thereof. Rather, fromthe position values and the detection times of the position values, theclock pulse for one processing station each is generated in the centralcontroller. In particular, the thus generated clock pulse takes intoaccount fluctuations of the rotation of the respective object to beprocessed, whereby an exact activation of the processing station isenabled by this clock pulse.

Furthermore, fluctuations and positioning errors of the movements of therotary cycle apparatus may be compensated. Moreover, manufacturingtolerances of the rotary cycle apparatus may be compensated.

Positioning errors and manufacturing tolerances may be compensated bysuitably presetting starting signals for the respective clock pulse.Fluctuations of movement of the rotary cycle apparatus during processingof the objects are compensated by suitably presetting the clock pulseitself.

It is particularly advantageous to detect such manufacturing tolerancesin a calibrating procedure in order to adapt the clock pulse generatedin the central controller as optimally as possible in order to eliminatesuch manufacturing tolerances.

In case of a conveying unit configured as a rotary cycle apparatus andprocessing stations configured as printing units, the calibratingprocedure may be performed as follows.

Rotationally symmetrical reference objects are supplied to theindividual printing units on rotatable supports of the rotary cycleapparatus. Thereby, all of the reference objects are supplied to all ofthe printing units, whereby suitable reference bar patterns are printedonto each of the reference objects. Subsequent thereto, determination ofthe manufacturing tolerance of the rotary cycle apparatus, especiallywith regard to the motion of rotation of the rotary cycle apparatus, iseffected by analyzing the printed reference bar patterns. In thesimplest case, the analysis is effected in such a manner that therotationally symmetrical reference objects are cut open. Thus, thesurface areas of the reference objects may be spread out into a surfaceplane so that the reference bar patterns applied thereto may beevaluated by means of a microscope.

In particular, the clock pulse may be configured as a series of countingpulses, which are generated in a frequency generator for activating theprocessing station in dependence upon control commands from the centralcontroller.

The output signals of the frequency generators may be re-read into thecentral controller. Therein they constitute input quantities of controlloops for generating the counting pulses for the individual processingstations. In this manner also fluctuations of the cycle andcomponent-induced fluctuations of the output signals of the frequencygenerators may be compensated by means of the central controller.

The invention will be explained hereinafter with reference to thedrawings, in which

FIG. 1 shows a schematic representation of an embodiment of a device forprocessing the surface of objects;

FIG. 2 shows a block diagram of the components of a first embodiment ofthe control means for the device according to FIG. 1; and

FIG. 3 shows a block diagram of the components of a second embodiment ofthe control means for the device according to FIG. 2.

FIG. 1 schematically shows the structure of an embodiment of a device 1for processing the surface of objects 3. The device 1 comprises aconveying unit, by means of which the objects 3 are supplied todifferent processing stations B₁-B₈.

In the present case, the conveying unit is configured as a rotary cycleapparatus 2, on which a total of eight objects 3 to be processed isspaced equidistantly in the circumferential direction. In accordancewith the number of objects 3 placed on the rotary cycle apparatus, atotal of eight processing stations B₁-B₈ is provided, which are arrangedin the circumferential direction of the rotary cycle apparatus 2. Via aconveyor drive means (not shown), the rotary cycle apparatus 2 isrotated in angular steps Δα=45°, whereby all the objects 3 aresimultaneously transported to the respectively next processing stationon the rotary cycle apparatus 2.

In the present case, the objects 3 to be processed are configuredrotationally symmetrical and may for example comprise beverage cans,cups or beverage bottles. The rotationally symmetrical objects 3 areeach fixed on a rotatably journalled support 4. The supports 4 aredriven by drive means, which are not shown in FIG. 1, so that theobjects 3 each perform a rotation about their axis of symmetry. Thedrive means are firmly connected to their respective supports 4 and aremoved along upon rotation of the rotary cycle apparatus 2.

In the present case, the device 1 serves for printing the objects 3carried on the rotary cycle apparatus 2. One of the processing stationsB₁ is configured as a loading station, by means of which the objects 3are supplied to the rotary cycle apparatus 2. Moreover, one of theprocessing stations B₈ is configured as an unloading station, by meansof which the processed objects 3 may again be removed from the rotarycycle apparatus 2.

The processing station B₂ following the loading station in the directionof transportation of the rotary cycle apparatus 2 is constituted by afirst inspection unit, by means of which a pre-inspection of the objects3 to be processed is performed. It is particularly advantageous toconfigure the inspection means as an image processing system.

In the direction of transportation of the rotary cycle apparatus 2, theinspection unit is followed by four processing stations which areconfigured as printing stations B₃-B₆. The first printing unit B₃ isoperated in accordance with a contact method, for example a silk screen,offset printing, flexographic printing or intaglio printing method, andcomprises a separate printing roller 5 for this purpose, by means ofwhich prints are applied to the surfaces of the objects 3.

The further three printing units B₄-B₆ are operated in accordance withcontact-free methods. These units comprise one inkjet printing head 6each, which is not illustrated separately. Preferably, printing patternsof different colors are applied to the surfaces of the objects 3 bythose printing units. In principle, also laser machining apparatuses andthe like may be employed.

Finally, a further inspection unit for controlling the processed objects3 is provided as a last processing station B₇ in advance of theunloading station. Advantageously, also this inspection unit isconfigured as an image processing system.

In general, the design of the device 1 may vary with regard to theconfiguration, number and arrangement of the processing stations B₁-B₈at the rotary cycle table. Accordingly, other conveying means, such aslinear conveyors, may also be provided instead of rotary cycleapparatuses 2.

FIG. 2 shows a first example of the components for the control of device1 according to FIG. 1. The drive means for rotation of the objects 3 andthe processing stations B₁-B₈ for performing processing processes, i.e.the printing units and inspection units in the present case, arecontrolled by a central controller 7. The central controller 7 comprisesa microprocessor system, which is not shown. Furthermore, it alsocomprises connections, which are also not shown, in the form of inputsand outputs for connecting the individual components of the device 1.Finally, the central controller 7 comprises an oscillator (not shown),by means of which a lead frequency is generated. The lead frequency maypreferably be parameterized. Particularly advantageously, the leadfrequency may be varied by frequency division.

The lead frequency generated in the central controller 7 is output tothe drive means and the processing stations B₁-B₈ for synchronizationthereof. Such a synchronization of the processing stations B₁-B₈ to thedrive means is necessary so that the objects 3 may be positioned exactlyin predetermined rotary positions at the respective processing stationsB₁-B₈, wherein the respective processing processes are performed by theprocessing stations B₁-B₈.

As can be seen from FIG. 2, the central controller 7 is connected to acomputing unit 9 via first connecting means 8, which computing unitserves for controlling the rotation of the objects 3 on the rotary cycleapparatus 2. The computing unit comprises, analogous to the centralcontroller 7, a microprocessor system and an array of inputs andoutputs.

The drive means for the rotation of the objects 3, which drive means areeach constituted by an amplifier 11 and a motor 12, as well asincremental encoders 13 for detecting the current rotary position of therespective supports 4 for the objects 3 are connected to the computingunit via second connecting means 10 a, 10 b.

Finally, the processing stations B₁-B₈ are connected to the centralcomputing unit 9 via third connecting means 14.

In a first advantageous embodiment, the computing unit 9 is arranged onthe rotary cycle apparatus 2 and moves along therewith. In this case,the second connecting means 10 b, 10 b for coupling the computing unit 9to the drive means and the incremental encoders 13 may be constituted bycables, since the drive means and the incremental encoders 13 are movedalong with the rotary cycle apparatus 2 as well.

Contrary thereto, a contact-free transmission of data is effectedbetween the stationary arranged central controller 7 and the computingunit 9 via the first connecting means 8. In this case, the firstconnecting means 8 may be constituted by slip rings, optical data linksor the like.

In a second embodiment, the computing unit 9 is stationary arranged. Inthis case, the first connecting means 8 may be constituted by cables,whereas the second connecting means 10 a, 10 b form data links forcontact-free transmission of data.

The drive means for the rotation of the objects 3 are controlled orregulated, respectively, in dependence upon the lead frequency. Inprinciple, the drive means may comprise suitable stepper motors for thispurpose. Particularly advantageously, position control of the drivemeans is effected in dependence upon the signals generated by therespective incremental encoder 13.

For synchronizing the processing stations B₁-B₈ to the drive means, theprocessing processes of the processing stations B₁-B₈ are alsocontrolled by presetting the lead frequency. By means of the centralcontroller 7, starting signals are computed in dependence upon thedetected rotary positions of the respective objects 3 to be processedand output to the respective processing stations B₁-B₈ for triggering aprocessing process. Moreover, the duration of a processing process ispredetermined by the central controller 7 by inputting the leadfrequency into the respective processing station B₁-B₈ for thecorresponding time interval only.

In a processing station B₁-B₈ configured as an inspection unit, theinspecting procedure of the objects 3 is controlled by presetting thelead frequency. In case the inspection unit comprises an imageprocessing system, the lead frequency serves for triggering the imaging.

For taking still pictures, counters are activated and deactivated by thelead frequency, whereas when taking motion pictures, the lead frequencypredetermines the imaging frequency. Generally, further inspection unitsmay be activated by the lead frequency as well, which units comprisestroboscopes and the like.

In the processing stations B₁-B₈ configured as printing units, theprinting processes are controlled in dependence upon the lead frequency.In the printing unit comprising the printing roller 5, the movementthereof is predetermined by the lead frequency. In particular, it servesfor triggering counters, wherein the contact pressure and imprint of theprinting roller 5 on the respective object 3 is controlled in dependenceupon the counting signals.

In the contact-free operating printing units, the inkjet printing heads6 are controlled in dependence upon the lead frequency. The leadfrequency is conveniently adapted to the output frequency of inkjetdroplets, the so-called dot frequency, of the inkjet printing head 6.

On the one hand, the lead frequency may be selected such that it exactlycorresponds to the dot frequency.

On the other hand, the lead frequency may also be selected higher thanthe dot frequency, wherein the lead frequency is higher than the dotfrequency, for example, by a factor 2^(N) (N =1, 2 . . . ). Thus,especially offset values of the printing procedures with the variousinkjet printing heads 6 may be adjusted in a better way. For the aboveexample of a lead frequency being higher by 2^(N), the offset of theprinting with two different colors, which is performed with twodifferent inkjet printing heads 6, may be adjusted with a resolution of½^(N) regarding a dot, i.e. an inkjet droplet.

FIG. 3 shows a further example of the components for the control ofdevice 1 according to FIG. 1. The components have a largely comparablestructure and a largely analogous function with respect to theembodiment according to FIG. 2.

In the embodiment according to FIG. 3, the central controller 7 isconnected to an evaluation unit 15 via the first connecting means 8,wherein said evaluation unit comprises a structure corresponding to thecomputing unit 9.

Analogous to the embodiment according to FIG. 2, the drive means andincremental encoders 13 are connected to the evaluation unit 15 via thesecond connecting means 10 a, 10 b. In further correspondence to theembodiment according to FIG. 2, the evaluation unit 15 may be arrangedon the rotary cycle apparatus 2 or arranged stationary. Accordingly,either the first connecting means 8 or second connecting means 10 a, 10b are constituted by contact-free operating data links, wherein therespective other connecting means 10 a, 10 b, 8 may be formed by cables.

The drive means for the rotation of the objects 3 are triggered independence upon the signals of the respective incremental encoders 13via the evaluation unit 15. Preferably, position control loops foractivating the drive means are integrated in the evaluation unit 15.

The signals of the incremental encoders 13 are further continuouslydetected and stored in the evaluation unit 15. A cyclic anddeterministic reading of the incremental encoders 13 is effected suchthat not only the respective position values, but also the detectiontimes of the position values are detected and stored in sets of data inthe evaluation unit 15.

From said data sets an individual clock pulse is generated in thecentral controller 7 for each processing station B₁-B₈. At first, it isdetected by the central controller 7, which one of the objects 3 ispositioned at the respective processing station B₁-B₈ to be triggered.Then, a clock pulse is generated from the data sets for the incrementalencoder 13, which data sets are associated to this object 3 and whichclock pulse follows the signals of this incremental encoder 13. Thus,the processing station B₁-B₈ is activated in synchronism to the rotationof the respective object 3. Since the data sets comprise the positionvalues and the detection times of the position values of the incrementalencoder 13, the movement thereof is completely detected, whereinespecially also fluctuations of the signals may be detected and takeninto account. The individual clock pulse generated in dependence uponthose signals for the respective processing station Bl-B₈ thus ensures aprocessing process running exactly synchronously to the rotation of theobject 3.

In the present case, frequency generators 16 are arranged in advance ofthe individual processing stations B₁-B₈, which generators are connectedto the central controller 7 via connecting leads 17. The output signalsof the frequency generators 16 are re-read into the central controller 7via further leads 18.

The clock pulse generated for a processing station B₁-B₈ is comprised ofa series of counting pulses, which are generated in the respectivefrequency generator 16 in dependence upon control commands generated inthe central controller 7. The frequency generator 16 in turn controlsthe processing process in the subsequently arranged processing stationB₁-B₈ by means of the counting pulses in accordance with the embodimentof FIG. 2.

The re-read output signals of the frequency generator 16 areadvantageously used for correcting any errors, which may be caused byfluctuations in the cycle time of the central controller 7 or bycomponent-induced fluctuations of the output signals of the frequencygenerator 16.

The re-read output signals of a frequency generator 16 constituteinstantaneous values for a control loop, which are compared topredefined set-point values in the central controller 7. The intervalsof the counting pulses generated in the frequency generators aresignificantly shorter than the cycle time of the central controller 7.

LIST OF REFERENCE NUMERALS

-   (1) Device-   (2) Rotary cycle apparatus-   (3) Object-   (4) Support-   (5) Printing roller-   (6) Inkjet printing head-   (7) Controller-   (8) First connecting means-   (9) Computing unit-   (10 a, 10 b) Second connecting means-   (11) Amplifier-   (12) Motor-   (13) Incremental encoder-   (14) Third connecting means-   (15) Evaluation unit-   (16) Frequency generator-   (17) Connecting lead-   (18) Lead-   (B₁-B₈) Processing station

1. A device for processing the surface of an object comprising, aconveying unit, by which said objects are transported into desiredpositions at said processing stations; a central controller, by whichthe functions of said conveying unit and of said processing station aresynchronized by a clock pulse correlated with transport of said objectand wherein said central controller controls each processing station. 2.The device according to claim 1,wherein said processing stations furthercomprises a printing unit.
 3. The device according to claim 2,wherein atleast one of said printing units further comprises an inkjet printinghead.
 4. The device according to claim 3, wherein at least one of saidprinting units further comprises a printing roller.
 5. The deviceaccording to claim 3, wherein at least one of said processing stationsfurther comprises an inspection unit.
 6. The device according to claim1,wherein said obiects are symmetrical about a rotational axis.
 7. Thedevice according to claim 6, wherein said objects are selected from thegroup consisting of beverage cans, beverage bottles or cups.
 8. Thedevice according to claim 1, wherein said conveying unit comprises arotary cycle apparatus, on which said objects are arranged in thecircumferential direction and may each be set into rotation by means ofa conveyor drive means.
 9. The device according to claim 8, wherein saidobjects are each rotationally journalled with respect to their axis ofrotation.
 10. The device according to claim 1, wherein starting signalsare generated in the central controller, by which the individualprocessing stations may be started independently.
 11. The deviceaccording to claim 1, wherein by predetermining the duration of thetransmission of said clock pulse to a processing station, the durationof the function of said processing station may be predefined by thecentral controller.
 12. The device according to claim 11, wherein atleast one incremental encoder is provided for detecting the rotaryposition of said objects.
 13. The device according to claim 12, whereinsaid conveyer drive means generate rotation in dependence upon thesignals of said incremental encoder are position controlled.
 14. Thedevice according to claim 13, wherein a lead frequency defining theclock pulse may be preset by said central controller.
 15. The deviceaccording to claim 14, wherein said lead frequency may be adjusted. 16.The device according to claim 14, characterized in that said leadfrequency is transmitted to a computing unit for synchronizing therotation of said objects generated by said conveyer drive means to saidprocessing stations.
 17. The device according to claim 16, wherein saidcomputing unit is stationary.
 18. The device according to claim 16,wherein said computing unit is arranged on said rotary cycle apparatus19. The device according to claim 16, wherein said lead frequency andthe signals of said incremental encoders constitute input quantities forthe position control of the respective conveyer drive means.
 20. Thedevice according to claim 16, wherein said lead frequency may be adaptedto the operating frequencies of said processing stations.
 21. The deviceaccording to claim 20, wherein said lead frequency is an operatingfrequency of inkjet droplets of an inkjet printing head.
 22. (canceled)23. (canceled)
 24. (canceled)
 25. (canceled)
 26. (canceled) 27.(canceled)
 28. (canceled)
 29. A device for processing the surface of anobject comprising; at least one processing station; a conveying unit, bywhich said object is transported into desired positions at saidprocessing station; a central controller, by which the functions of saidconveying unit and said processing stations are synchronized bypresetting a clock pulse being correlated with the transport of saidobject, and wherein said central controller controls for each processingstation; and, wherein said clock pulse is derived from the cyclicallyand currently detected position values and detection times of theposition values derived from the transport of the object beingprocessed.
 30. The device according to claim 29, wherein the positionvalues and the detection times of the position values of said objectsare detected by an incremental encoder and stored as data sets in anevaluation unit.
 31. The device according to claim 30, wherein saidclock pulse for a processing station comprises a series of countingpulses derived from the data sets stored in said evaluation unit andfollow the increments of the respective incremental encoder.
 32. Thedevice according to claim 31, wherein said counting pulses are generatedin a frequency generator controlling a processing station.
 33. Thedevice according to claim 32, wherein the output signals generated bysaid frequency generator are re-read into said central controller. 34.The device according to claim 33, wherein control loops for generatingsaid counting pulses are provided in said central controller, andwherein said re-read output signals of said frequency generatorsconstitute instantaneous values of said control loops.
 35. The deviceaccording to claim 31, wherein the intervals of the individual countingpulses are shorter than the cycle time of said central controller.